the sheer number of possible answers is overwhelming, but pretty much everything Google does fails, except for search and email. (I can't be the only one who's afraid to find out what their cars are like.) so I'm going to say the reason Google Wallet failed is because it was neither search nor email.
I guess you could say Android is only half a failure, because the constant catch-up game they're playing with Apple isn't going as badly as the constant catch-up game Google Plus (and Wave, and whatever they called the other one) plays with Facebook.
but seriously, business failure can happen for so many reasons, it doesn't really mean anything at all, unless of course you see a string of people failing at the same thing.
I guess you could say Android is only half a failure, because the constant catch-up game they're playing with Apple isn't going as badly as the constant catch-up game Google Plus (and Wave, and whatever they called the other one) plays with Facebook.
but seriously, business failure can happen for so many reasons, it doesn't really mean anything at all, unless of course you see a string of people failing at the same thing.